This invention relates to a method of coating core samples and more particularly to a method of applying an epoxy resin coating to core samples removed from well boreholes.
In the drilling of oil and gas wells, for example, it is customary, when the drilling bit approaches an underground formation that may contain oil or gas, to take core samples of the strata traversed during the ensuing drilling. These samples are brought to the surface and analyzed for such characteristics as lithology, porosity, permeability, compressibility, oil and water saturation, etc., and the resulting data is used to determine whether the underground formation is capable of producing oil or gas on a commercially acceptable basis and for reservoir evaluation.
The various characteristics of the core sample are measured with the sample mounted in a core holder, illustratively of the triaxial type, which has various pressure and other connections for making the desired measurements. The sample is positioned within the holder in a deformable rubber or plastic sleeve, and a confining pressure is applied to the sleeve which may approximate the underground effective overburden pressure to which the sample had been subjected prior to its removal from the borehole. While it is desirable to have such core analyses performed reasonably promptly after the removal of the samples from the borehole so that the data obtained may be utilized in determining whether further drilling is needed or whether the well may be completed for production at the horizon already reached, it is customary to retain the sample so that it will be available for subsequent inspection and analysis perhaps even years after the drilling of the well. Accordingly, extensive storage facilities often are provided for maintaining and preserving the samples recovered from wells so they may be examined and subjected to further testing by geologists or other testing personnel.
Heretofore, difficulties have been encountered in the realization of accurate and reliable measurements of the various characteristics of core samples of this general type. As an illustration, the comparatively high confining pressure applied to the core holder sleeve on occasion urged the sleeve into the exposed pores of the sample, with a resulting adverse affect on porosity and other measurements. As another illustration, and this has been a special moment in cases in which the sample was stored for a period of time, grains at the surface of the sample became loose during repeated handling and further interfered with the desired measurements. In addition, the samples often would not fit with the necessary precision in the thick-wall steel molds used for uniaxially confined sample tests.